Zn 3 V 4 (PO 4 ) 6 : A New Rocking-Chair-Type Cathode Material with High Specific Capacity Derived from Zn 2+ /H + Cointercalation for Aqueous Zn-Ion Batteries.

Phosphate cathode materials with a stable and open framework structure are expected to be one of the favorable cathode materials for aqueous zinc-ion batteries (AZIBs). However, the slow migration rate of Zn and complex mechanism in aqueous electrolyte are serious problems that limit their application at the present. Here, a new rocking-chair-type cathode material ZnV(PO)@C (ZVP@C) for AZIBs is synthesized for the first time and evaluated using a composite carbon coating to improve the electronic conductivity. Benefiting from the two-electron reaction of vanadium and the cointercalation of Zn/H, ZVP@C/30%BP delivers a specific capacity as high as 120 mAh·g at 0.04 A·g. A good capacity retention of 80% after 400 cycles at 1 A·g is also obtained, which is attributed to the stable crystal structure and the cointercalation reaction of Zn/H. The reaction mechanism is investigated by X-ray diffraction (XRD), XRD, X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDS). This work not only provides a new phosphate cathode material for AZIBs but also gives a new strategy for improving the specific capacity of phosphate cathode material.